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journal of Asian Ceramic Societies xxx (2017) xxx-xxx
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SJ ceramic Journal of Asian Ceramic Societies
journal homepage www.elsevier.com/locate/jascer
JAsCerS
1 Full Length Article
2 Effect of nanoclay on durability and mechanical properties of flax
3 fabric reinforced geopolymer composites
4 Q1 H. Assaedia b, F.U.A. Shaikhc, I.M. Low3 *
5 Q2 a Department of Imaging & Applied Physics, Curtin University, GPO Box U1987, Perth, WA 6845, Australia
6 b Department of Physics, Umm Al-Qura University, P.O. Box 715, Makkah, Saudi Arabia
7 Q3 c Department of Civil Engineering, Curtin University, GPO Box U1987, Perth, WA 6845, Australia
ARTICLE INFO
ABSTRACT
20 21 22 23
Article history: Received 12 August 2016 Received in revised form 15 November 2016 Accepted 10 January 2017 Available online xxx
Keywords:
Geopolymer
Nanoclay
Mechanical properties Flax fibres Durability
The main concern of using natural fibres as reinforcement in geopolymer composites is the durability of the fibres. Geopolymers are alkaline in nature because of the alkaline solution that is required for activating the geopolymer reaction. The alkalinity of the matrix, however, is the key reason of the degradation of natural fibres. The purpose of this study is to determine the effect of nanoclay (NC) loading on the mechanical properties and durability of flax fabric (FF) reinforced geopolymer composites. The durability of composites after 4 and 32 weeks at ambient temperature is presented. The microstructure of geopolymer matrices was investigated using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The results showed that the incorporation of NC has a positive impact on the physical properties, mechanical performance, and durability of FF reinforced geopolymer composites. The presence of NC has a positive impact through accelerating the geopolymerization, reducing the alkalinity of the system and increasing the geopolymer gel.
© 2017 The Ceramic Society of Japan and the Korean Ceramic Society. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/
licenses/by-nc-nd/4.0/).
25 1. Introduction
26 Ordinary Portland Cement (OPC) is believed to be responsible of
27 generating 5% of the global carbon dioxide emission [1]. One of the
28 most attractive alternatives of OPC is geopolymer binder due to its
29 comparable mechanical properties to the OPC. The development
30 of geopolymer concrete is not only important because they are
31 environmental friendly materials, but also due to their wide range
32 of raw waste materials to produce worthy construction matrices,
33 resulting in low cost material with similar mechanical properties
34 to that of cement concrete [2]. Geopolymers are produced by acti-
35 vating a solid aluminosilicate source such as coal derived fly-ash,
36 meta-kaolin and slag with alkaline solutions, amorphous networks
37 of tetrahedral SiO4 and AlO4 connected by sharing oxygen atoms 38Q4 [3]. The formation of geopolymer gel can be described by Eq. (1)
39 [3].
Hitherto, nanomaterials have received increased attention 41
in geopolymer and cement research; especially in producing 42
nanocomposites that possess superior mechanical properties [4-6]. 43 Several kinds of nanomaterials have been incorporated efficiently 44
in geopolymer pastes. For instance, it has been found that nano- 45
silica and nano-alumina particles have the ability to reduce the 46
porosity and water absorption of geopolymer matrices [6]. In 47
another study [7], nano-alumina and nano-silica particles have 48 been incorporated in geopolymer matrices giving them higher 49
mechanical performance. The nanoparticles are not only acting 50
as fillers, but also enhancing the geopolymeric reaction. A fur- 51
ther study on the effect of adding carbon nanotubes (CNT) to 52
flyash-based geopolymer has shown an increase in the mechani- 53
cal and electrical properties of geopolymer nano-composites when 54 compared to the control paste [8]. Wei and Meyer reported the
n(Si2O5, Al2O2)+ 2nSiO2+ 4nH2O+ NaOH ^ Na++ n(OH)3 -Si -O-
-O- Si -(OH)3
* Corresponding author. Fax: +61 8 9266 2377. E-mail address: j.low@curtin.edu.au (I.M. Low).
properties of cement/nanoclay composites, where the nanoparti-cles reduce the porosity of cement matrices, as well as improve the strength of cement matrix through pozzolanic reactions [9].
http://dx.doi.0rg/10.10i6/j.jascer.2017.01.003
2187-0764/© 2017 The Ceramic Society of Japan and the Korean Ceramic Society. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
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59 Farzadnia et al. [10] reported that incorporation of 3wt% hal-
60 loysite nanoclay into cement mortars increased the compressive
61 strength by up to 24% compared to the control sample. In a pre-
62 vious study, we investigated the effect of nanoclay (Cloisite 30B)
63 on the mechanical and thermal properties of geopolymer compos-
64 ites [11]. Nanoclay particles were found to help developing denser
65 geopolymer matrices, thereby producing geopolymer with supe-
66 rior mechanical performance.
67 Despite the potential improvement of properties of geopoly-
68 mers, the geopolymer matrix still suffers from brittle failure readily
69 under applied force and generally exhibits low mechanical strength
70 [12,13]. One way to resolve this limitation is through utilizing
71 natural fibres to fabricate fibre-reinforced geopolymer compos-
72 ites. The advantages of using natural fibres in composites include
73 the low density, flexibility and the high specific modulus [14,15].
74 Cotton fibres and fabrics have been used to improve the fracture 75Q6 toughness and mechanical performance of geopolymer compos-
76 ites [16,17]. Also, flax and wool fibres have presented positive
77 effects when incorporated in geopolymer matrices; they signif-
78 icantly improved the mechanical properties of the natural fibre
79 reinforced geopolymer composites [[18]—1]. In our previous work,
80 geopolymer composites were reinforced with woven flax fabric and
81 tested for mechanical properties such as flexural strength, flexural
82 modulus, compressive strength, hardness, and fracture toughness.
83 The results showed that all mechanical properties were improved
84 by increasing the flax fibre contents, and showed superior mechan-
85 ical properties over the pure geopolymer matrix [19]. In a further
86 study, geopolymer matrices were reinforced with a combination of
87 nanoclay (NC) and flax fabrics (FF) and it was found that the addition
88 of NC to geopolymers improved the adhesion between the natural
89 fibres and the matrices due to the high amount of geopolymer gel
90 formed, resulting in higher mechanical results [20].
91 However, there are concerns in utilizing natural fibres in alkali-
92 based matrices. The main concern is regarding the long-term
93 durability of natural fibre reinforced composites. Natural fibres can
94 be degraded and damaged in high-alkaline environment; thereby
95 adversely affecting the mechanical properties and durability of the
96 composites [21-23]. Natural fibre degradations in alkaline environ-
97 ments was studied by Gram [24] and he described the degradation
98 mechanism as the decomposition of hemicellulose and linen which
99 leads to the splitting of natural fibres into micro-fibrils [24]. This
100 effect has been observed using SEM in the case of jute fibres in
101 cement matrix, where the natural fibres split-up and fibrillised
102 resulting in reduction in the tensile strength of jute fibres by 76% 10Q7 [25]. To reduce the degradation impact, nanoparticles can play an
104 important role. The effect of nanoclay particles on the durability
105 of flax fibres reinforced cement composites at 28 days and after
106 50 wet/dry cycles has been investigated by Aly et al. [21]. Samples
107 loaded with 2.5 wt% nanoclay particles showed lower deterioration
108 in the flexural strength when compared to its counterpart con-
109 trol samples. This was attributed to the effect of nanoparticles in
110 reducing the degradation of flax fibres.
111 According to the best of knowledge of authors, no study has been
112 reported on the durability of natural fibres in geopolymer matri-
113 ces. The presence of nanoclay particles is anticipated to reduce
114 the degradation of natural fibres by consuming certain amounts
115 of alkaline solution, which reduces the alkalinity of the medium.
116 Nanoclay is also expected to produce higher amount of geopoly-
117 mer gel, increases in matrix density, fibre-matrix adhesion, and the
118 concomitant improvement in mechanical properties. In this paper,
119 in order to improve the durability and reduce the degradation of
120 flax fabric (FF) in geopolymer composites, geopolymer matrices
121 were modified by the addition of nanoclay (NC) particles. This study
122 presented the effect of different loadings of nanoparticles on the
123 durability and mechanical properties of FF-reinforced geopolymer
124 nanocomposites. The medium to long term durability of all samples
Table 1
Formulation of samples. Each samples is a mix of: 1.0kg Eraring flyash, 214.5g Q10 sodium hydroxide (8 M) and 535.5 g sodium silicate.
Sample NC (g) FF (layers)
GP 0 0
GPNC-1 10 0
GPNC-2 20 0
GPNC-3 30 0
GP/FF 0 10
GPNC-1/FF 10 10
GPNC-2/FF 20 10
GPNC-3/FF 30 10
has been discussed in terms of flexural strength obtained at 4 and 125
32 weeks. The microstructure was investigated using X-ray diffrac- 126
tion, Fourier transform infrared spectroscopy (FTIR) and scanning 127
electron microscopy (SEM). 128
2. Experimental procedure 129
2.1. Materials 130
Low-calcium flyash (ASTM class F) with specific gravity 2.1 131
obtained from the Eraring power station in NSW was used to pre- 132
pare the geopolymeric nano-composites. The alkaline activator for 133
geopolymerisation was a combination of sodium hydroxide solu- 134
tion and sodium silicate grade D solution. Sodium hydroxide flakes 135
with 98% purity were used to prepare the solution. The chemical 136
composition of sodium silicate used was 14.7% Na2O, 29.4% SiO2 137
and 55.9% water by mass. 138
Flax fabric (FF) and nanoclay (Cloisite 30B) were used for the 139
reinforcement of geopolymer composites. The fabric, supplied by 140
Pure Linen Australia, is made up of yarns with a density of 1.5 g/cm2. 141
The nanoclay (NC) with specific gravity of 1.98 has been provided 142
by Southern Clay Products, USA. 143
To prepare the geopolymer pastes, an alkaline solution to fly 144
ash ratio of 0.75 was used and the ratio of sodium silicate solution 145
to sodium hydroxide solution was fixed at 2.5. The concentration 146
of sodium hydroxide solution was 8 M, which was prepared and 147
combined with the sodium silicate solution one day before mixing. 148
2.2. Preparation of geopolymer nanocomposites 149
The nano-clay particles (NC) were added to the flyash at the 150
loadings of 1.0, 2.0 and 3.0% by weight. The flyash and nanoparti- 151
cles were first dry mixed for 5 min in a covered mixer at low speed 152
and then mixed for another 10 min at high speed until homogene- 153
ity was achieved. The alkaline solution was then added slowly to 154
the flyash/nanoparticles mixture in a Hobart mixer at a low speed 155
until the mixture became homogeneous, followed by further mix- 156
ing for another 10 min on high speed. The resultant mixture was 157
then poured into wooden moulds. The wooden moulds were then 158
placed on a vibration table for 2 min before they were covered with 159
a plastic film and cured at 80°C for 24 h in an oven before demolding. 160
2.3. Preparation of FF-composite and nanocomposites 161
Similar mixtures were prepared to produce the FF- 162
nanocomposites. Four samples of geopolymer pastes reinforced 163
with ten layers of FF (see Table 1) were prepared by spreading 164
a thin layer of the paste in a well-greased wooden mould and 165
carefully placing the first layers of FF on it. The fabric was fully 166
saturated with the paste by a roller, and the process repeated for 167
ten layers; each specimen contained a different weight percentage 168
of nanoclay particles. The samples were then left under heavy 169
weight (20 kg) for 1 h to reduce entrapped air inside the samples. 170
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All samples were covered with plastic film and cured at 80° C for 24 h in an oven before demoulding. They were then dried under ambient conditions for 28 days.
All samples were then categorized in two series. In the first series, samples were cured under ambient conditions to be tested after 4 weeks, and the samples of second series were stored in the same condition for 32 weeks. The formulation of samples is given in Table 1.
2.4. Characterization
The samples were crushed and ground to fine powder. They were then measured on a D8 Advance Diffractometer (Bruker-AXS, Germany) using copper radiation and a LynxEye position sensitive detector. The diffractometer were scanned from 7.5° to 60° using a scanning rate of 0.5°/min. XRD patterns were obtained by using Cu ka lines (k = 1.5406 A). Crystalline phases were identified using software EVA version 11. The chemical compositions of NC were analyzed using X-ray fluorescence (XRF). XRF was outsourced to a commercial laboratory (Bureau Veritas, Perth). An FTIR scan was performed on a Perkin Elmer Spectrum 100 FTIR spectrometer in the range of 4000-500 cm-1 at room temperature. The spectrum was an average of 32 scans at a resolution of 2 cm-1, corrected for background. The microstructures of geopolymer composites were examined using Zeiss Neon focused ion beam scanning electron microscope (FIB-SEM). The specimens were mounted on aluminium stubs using carbon tape and then coated with a thin layer of platinum to prevent charging before observation.
2.5. Physical and mechanical properties
Measurements of bulk density and porosity were conducted to define the quality of geopolymer nanocomposite. Density of samples (p) with volume (V) and dry mass (md)was calculated using Eq. (2):
Table 2
Density and porosity for pure geopolymer and geopolymer nano-composites.
p = md
The value of apparent porosity (Pa) was determined using Archimedes' principle in accordance with the ASTM Standard (C-20) [26]. Pure geopolymer and nano-composite samples were immersed in clean water, and the apparent porosity (Pa) was calculated using Eq. (3):
Pa = ma -md X 100
where ma is mass of the saturated samples in air, and mw is mass of the saturated samples in water.
A LLOYD Material Testing Machine (50 kN capacity) with a displacement rate of 0.5 mm/min was used to perform the mechanical tests. Rectangular bars of 60 x 18 x 15 mm3 were cut from the fully cured samples for three-point bend test with a span of 40 mm to evaluate the flexural strength and modulus. Five samples of each group were used to evaluate the flexural strength and flexural modulus of geopolymer composites. The values were recorded and analyzed with the machine software (NEXYGENPlus) and average values were calculated. The flexural strength (cF) was determined using the equation [27]:
of = ~
where Pm is the maximum load, S is the span of the sample, D is the specimen width, and W is the specimen thickness.
Sample Density (g/cm3) Porosity (%)
GP 1.84 ± 0.02 22.2 ± 0.4
GPNC-1 1.92 ± 0.02 21.3 ± 0.3
GPNC-2 2.05 ± 0.02 20.6 ± 0.3
GPNC-3 1.98 ± 0.03 21.0 ± 0.2
Values of flexural modulus (Ef) were computed using the initial slope of the load displacement curve (AP/AX) using the equation [27]:
4 WD3 \AX; 3. Results and discussion
3.1. Density and porosity
The results of porosity and water absorption of geopolymer paste and geopolymer nano-composites are shown in Table 2. Geopolymer nanocomposites revealed denser matrices and lower porosities when compared to the control sample. The addition of NC has increased the density and reduced the porosity of geopolymer nano-composites when compared to control geopolymer paste. The optimum addition was found as 2.0 wt% of NC, which increased density by 11.4% and reduced the porosity by 7.2% when compared to the control paste. This implies that the nanoparticles played a pore-filling role to reduce the porosity of geopolymer composites. However, adding excessive amounts of NC increased the porosity and decreased the density of all samples due to agglomeration of NC particles [11]. This finding is comparable with the study where the porosity of cement paste is decreased due to addition of 1.0% wt. of NC to cement paste; however, the porosity is increased because of the agglomeration effect when more nanoparticles were added [28].
3.2. X-ray fluorescence (XRF) and X-ray diffraction (XRD)
The chemical composition and loss on ignition of flyash and NC are shown in Table 3. Flyash and NC contain, in addition to silica and alumina, Fe2O3, CaO, K2O, Na2O, MgO and TiO2.
The XRD spectra of pure geopolymer and geopolymer nanocom-posites at 4 and 32 weeks are shown in Fig. 1(a-b) , respectively. The crystalline phases were indexed using powder diffraction files (PDFs) from the inorganic crystal structure database (ICSD). The diffraction patterns of the samples demonstrate some crystalline phases that were indexed distinctly: quartz [SiO2] (PDF 00-0461045) and mullite [Al2.32Si0.68O4.84] (PDF 04-016-1588). Quartz and mullite crystalline phases can be seen in all samples. According to Rickard et al. quartz and mullite are the main crystalline content of the Eraring flyash, and hence they are stable and unreactive in the alkaline environment. At 32 weeks, a new crystalline phase, trona [Na3H(Co3)2.2H2O] (PDF 00-029-1447), appears on the surface of geopolymer aged samples. Trona belongs to soda minerals group, which could be formed by the reaction of sodium hydroxide with water and carbon dioxide according to the chemical reaction [29]:
3NaOH + 2CO2 + 2H2O ^ Na3H(CO3)2 • 2H2O
The amorphous broad phase generated between 29 =17° and 30° for all samples reveals the reactivity of geopolymers. It is known that the amorphicity degree remarkably influences the mechanical properties of geopolymers. When the amorphous content is higher, the strength of geopolymers is similarly higher [30]. In previous study, it has been shown that the addition of nanoclay particles to geopolymer pastes increased the amorphous content of geopoly-
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Table 3
Chemical compositions of flyash and nanoclay (wt%).
SiO2 АЬОз CaO Fe2O3 K2O MgO Na2O P2O5 SO3 TiO2 MnO BaO LOI
Flyash 63.13 24.88 2.58 3.07 2.01 0.61 1.75 0.71 0.17 0.18 0.96 0.05 0.07 1.45
NC 47.05 16.24 0.29 3.42 0.03 0.19 0.01 0.11 0.08 0.00 0.00 30.61
Fig. 1. X-ray diffraction patterns of geopolymer and geopolymer nanocomposites at: (a) 4 weeks; (b) 32 weeks [legend: M = mullite, Q= quartz and T=trona].
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Fig. 2. FTIR spectra of geopolymer and geopolymer nanocomposites at: (a) 4 weeks; (b) 32 weeks.
274 mer nanocomposites, resulting in denser matrices and superior 3.3. FTIR observation
275 mechanical performance [11].
FTIR spectra of pure geopolymer and geopolymer nanocompos-ite at 4 and 32 weeks are shown in Fig. 2(a-b). The FTIR spectra of
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GP GPNC-1 GPNC-2 GPIMC-3
Flexural strength : Mat 4 weeks ■ at 32 weeks
Flexural modulus: * at 4 weeks at 32 weeks
Fig. 3. Flexural strength and modulus of geopolymer and nanocomposites at 4 and 32 weeks.
280 281 282
all samples shows a strong peak at ~1000 cm-1 which is attributed to Si—0—Si and Al—O—Si asymmetric stretching vibrations, which is the identification peak of the geopolymerisation [31,32]. A broad peak in the region around 3400 cm-1 indicates that the OH group is present attached to different centres (Al, Si) and free water [33,34]. The absorbance peak at 1640 cm-1 is also attributed to the (OH) bending vibration [35]. At 32 weeks changes have occurred, two peaks at 1420 and 1480 cm-1 appear indicating the presence of sodium carbonate; this was formed due to the atmospheric car-bonation on the matrices surfaces which confirms the XRD results [29]. During the ageing period the reaction has carried on at a low rate consuming more OH groups and forming stronger material. The water content decreased to some equilibrium level during this period resulting in lower broad peak at 3400 cm-1.
293 3.4. Flexural strength of geopolymer nanocomposites
The effect of ageing on the flexural strength and modulus of geopolymer matrices and nanocomposites is shown in Fig. 3. Overall, the incorporation of nanoclay into the geopolymer composite led to noteworthy improvement in the mechanical strength at all ages. At 4 weeks, the flexural strength of geopolymer nanocom-posite containing 1.0, 2.0 and 3.0wt.% NC was increased by 13.3, 24.4 and 15.5% respectively, while the flexural modulus improved by 16, 25 and 20%, respectively compared to the control sample. This enhancement noticeably shows the value of NC in supporting geopolymer reaction and filling the micro pores in the matrix [11-28]. Thus the microstructure of geopolymer nanocomposite is denser than the pure matrix, especially in the case of incorporating 2.0 wt.% NC, which is evident from its higher flexural strength and modulus. However, at 32 weeks, the flexural strength of nanocom-posites increased slightly compared to their values at 4 weeks. For instance, the flexural strength of GPNC-2 nanocomposite improved from 5.6 to 6.1 MPa by about 9% increase. This slight improvement
in the mechanical performance could be attributed to the slow reaction of free silica and alumina in the presence of Na+ ions during the ageing period [36,37]. In similar study, Hakamy et al. [23] reported that flexural strength of cement pastes containing 1.0% calcined nanoclay particles improved from 7.2 to 8.2 by about 7% after 236 days compared to its strength at 56 days. SEM images of the microstructure at 32 weeks of geopolymer paste and the geopolymer nanocomposite containing 2.0 wt.% NC are shown in Fig. 4(a-b) . For geopolymer matrix, Fig. 4a displays more pores showing a weak microstructure. On the other hand, Fig. 4b shows the SEM micrograph of GPNC-2 nanocomposite matrix, which is different from that of pure matrix, the microstructure is denser and more compact with fewer pores and more geopolymer gel.
3.5. Flexural strength of flax fabric reinforced geopolymer nanocomposites
The effect of ageing on the flexural strength and modulus of FF-reinforced geopolymer nanocomposites at 4 and 32 weeks is shown in Fig. 5. The incorporation of nanoclay into matrices led to enhancement in the flexural strength of all reinforced nanocomposites. For example, at 4 weeks, the flexural strength and modulus of GPNC-2/FF increased by 32.4% and 5.2%, respectively when compared to GP/FF composite. However, all composite showed reduction in the mechanical strength after 32 weeks. Fig. 6(a-b) shows the effect of ageing on the load-midspan deflection behaviour of GP/FF composites and GPNC-3/FF nanocomposites. The "ductile" behaviour can be observed in both composites with and without NC, with higher load capacity (about 29% increases) in the composite containing NC. It was observed that ductile behaviour is adversely affected and bending stresses are reduced due to degradation process. This decrease was attributed to the lignin and hemicellulose deterioration of flax fibre in matrix by Na+ ions attack and brittleness of the natural fibres due to the
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Fig. 4. SEM micrographs at 32 weeks of: (a) geopolymer paste, (b) nanocomposites containing 2.0 wt% NC.
343 mineralization of fibre cell wall in geopolymer pastes [38-40]. In
344 general, all natural fibres suffer various degree of deterioration
345 when exposed to alkaline environment [41]. This degradation in
346 alkali matrices ultimately led to weaken the fibre-matrix bonding,
347 and consequently reduced the mechanical performance of geopoly-
348 mer composites. The flexural strength of GP/FF composite dropped
349 to 23.0% of the initial strength at 4 weeks, whereas the flexural
350 strength of GPNC-1/FF, GPNC-2/FF and GPNC-3/FF nanocomposites
351 reduced by about 14.4%, 13.7% and 13.5% compared to its value
352 at 4 weeks. Based on this outcome, it can be concluded that the
353 reduction in the mechanical performance for nanocomposites was
354 less than the reduction of control sample composite after 32 weeks
355 ageing period. This may be attributed to the fact that nanoclay
356 particles consume amounts of the alkaline solution thus reduc-
357 ing the alkalinity of the medium, and producing higher amount of
358 geopolymer gel, which hence enhances the density of the matri-
359 ces and the fibre-matrix adhesion [20]. In a similar study, the
360 effect of calcined nanoclay on the durability of hemp fabric rein-
361 forced cement nanocomposites and the degradation of hemp fibres
362 are reported [23], the nanoparticles were found to improve the
363 durability and reduces the degradation of hemp fibres. In another
364 investigation, Aly et al. [21] reported that the addition of nanoclay
365 and waste glass to cement mortar could improve the durability and
366 mitigate the degradation of flax fibres implemented in the com-
367 posites by reducing the alkalinity of the matrix. Filho et al. [40]
368 investigated the durability of sisal fibre reinforced mortar with
369 the addition of metakaolin at 28 days and after 25 wet/dry cycles.
They observed that the flexural strength of metakaolin compos- 370
ites decreased by 23% when compared to its control composites at 371
28 days. They reported that 50% metakaolin replacement signifi- 372
cantly prevented the sisal fibres from the degradation in cement 373
matrix. In the current investigation, the NC effectively prevented 374 the flax fabric degradation by reducing the alkalinity of the matrix 375
through geopolymer reaction. Thus, the degradation of flax fibres 376
in nanocomposite was mostly reduced and the FF-nanocomposite 377
matrix interfacial bonding was typically improved. Fig. 7(a-b) 378
shows the changes in the fibres surface in GP/FF and GPNC-2/FF 379
at 4 weeks. The fibres look more regular and free of any signs 380
of degradation in both cases. After 32 weeks, however, the fibres 381
extracted from control specimen (Fig. 7c) reveal signs of degra- 382
dation and the fibrils are clearly splitting up, which influence the 383
flexural strength of the composite, whereas the fibres extracted 384
from GPNC-2/FF after ageing period (Fig. 7d) do not present signs 385
of significant damage. 386
4. Conclusions 387
Geopolymer composites and nanocomposites reinforced with 388
flax fabric (FF) and nanoclay (NC) have been fabricated and 389
characterized. The effect of NC on the durability of FF rein- 390
forced geopolymer nanocomposites and the degradation of FF 391
is reported. The optimum content of NC was 2.0 wt.%. After 32 392 weeks, the flexural strength of GP/FF composites decreased by 393
23.01% whereas flexural strength of GPNC-2/FF nanocomposites 394
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GP/FF GPNC-1/FF GPNC-2/FF GPNC-3/FF
Flexural strength : aat4weeks «at 32 weeks
Flexural modulus : -и-at 4 weeks -»-at 32 weeks
Fig. 5. Flexural strength and modulus of flax fabric reinforced geopolymer composites and nanocomposites at 4 and 32 weeks.
decreased by only 13.7%. SEM micrographs indicated that flax fibres in GP/FF composites suffer more degradation than that in GPNC-2/FF nanocomposites. Based on these observations, the addition of NC has great potential in improving the durability of flax fabric reinforced geopolymer nanocomposites during ageing.
Acknowledgement 400
The authors would like to thank Ms. E. Miller from the Depart- 401
ment of Applied Physics at Curtin University for the assistance with 402
SEM. 403
Fig. 6. Load versus mid-span deflection curves at 4 and 32 weeks for: (a) GP/FF composite; and (b) GPNC-3/FF nanocomposites.
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Fig. 7. SEM images of the flax fibres extracted from (a) GP/FF at 4 weeks, (b) GPNC-2/FF at 4 weeks (c) GP/FF at 32 weeks, and (d) GPNC-2/FF at 32 weeks.
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